Hemopoiesis is regulated by a large family of hemopoietic growth factors or interleukins (IL). Recent accumulating evidence suggests that molecules such as IL-6 and IL-lo, previously thought to act only on more differentiated cells, can also exert an influence on primitive hemopoietic progenitor cells. Whether these molecules have any effect on lymphoid-myeloid stem cells is not known. By developing strategies in transferring and expressing genes coding for these molecules in lymphoid-myeloid stem cells we attempt to study the extent to which they effect growth of these cells. We will also examine whether evolution of a specific lineage of cells from the lymphoid-myeloid stem cells can be determined by 1) tissue specific transcriptional signals placed in front of IL-6 cDNA, and 2) expression of genes coding for lineage- specific hemopoietic growth factors in addition to the inserted IL- 6 gene. These studies will provide important information as to how hemopoietic stem are being regulated by growth factors, singly or in concert with one another.